Interaction between Glyglu and Ca2+, Pb2+, Cd2+ and Zn2+ in solid state and aqueous solution.: Crystal structures of poly[aqua-1,2-κ-O-di[lead(gly-gluH)]bis(perchlorate)] and poly[bisglycylglutamic-cadmium(II) tetrahydrate]

Glycylglutamic acid (GEH2) is a peptide usually present in calcium binding sites. The interaction between the peptide and the cations Ca2+, Pb2+, Cd2+, and Zn2+ in aqueous solution and in the solid state is described. Six compounds were isolated with different protonation states of the ligand. Potentiometric equilibrium studies, 13C and 111Cd solid state CP MAS NMR and IR spectroscopy were performed. Two crystal structures are reported: [Pb(GEH)(H2O)1/2]ClO4 and [Cd(GEH)2]·3H2O. Both constitute 3D polymers, where only carboxylate groups are coordinated to the cations. The crystalline lead compound shows a hemidirected coordination sphere due to its stereochemically active lone pair. In deprotonated derivatives, it is possible to assign a metal-amino interaction to a far IR signal (340–370 cm−1).